A product called Diatomaceous Earth (which is just Diatom powder) is an organic substance you can either apply manually to the body of each chicken, or allow the chickens to dust bathe on their own in a mixture of it and soil. Diatomaceous Earth is derived from a type of algae and is abrasive and dehydrating to ectoparasites, creating a less hospitable living area for them on the bird's body.
